Simple signal transmission circuit capable of decreasing power consumption

ABSTRACT

A signal transmission circuit is formed by a transmitter, a receiver, a transmission line therebetween, and a bias circuit. The transmitter receives an input signal to transmit a signal corresponding to the input signal to the input of the transmission line. A voltage amplitude of the transmitted signal is smaller than a voltage amplitude defined by first and second power supply terminals. The receiver receives the transmitted signal, adjusts a voltage of the received signal in accordance with a bias voltage to generate a voltage adjusted signal, and wave-shapes the voltage adjusted signal to generate an output signal. The bias circuit differentially amplifies the output signal of the receiver and an inverted signal thereof to generate the bias voltage. The bias circuit includes a capacitor charged and discharged in accordance with the bias voltage.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a signal transmission circuit used between data line (or signal line) driver circuits of a display apparatus such as a liquid crystal display (LCD) apparatus.

[0003] 2. Description of the Related Art

[0004] Recently, in an LCD apparatus, a plurality of driver circuits such as data line driver circuits formed by large scale integrated (LSI) circuits are mounted on a glass substrate of an LCD panel by a chips-on-glass (COG) process or a system-on-glass (SOG) process. In this case, the data line driver circuits are arranged by a cascade connection method using aluminum connections therebetween. Therefore, since the aluminum connections have large resistances, high speed signal transmission circuits are required.

[0005] A first prior art signal transmission circuit is constructed by a transmitter formed by a CMOS inverter, a receiver formed by a CMOS inverter, and a transmission line therebetween. This will be explained later in detail.

[0006] In the above-described first prior art signal transmission circuit, however, the higher the frequency of a transmitted signal, the larger the power consumption.

[0007] A second prior art signal transmission circuit uses a reduced swing differential signaling (RSDS) method in conformity with the interface standard of National Semiconductor INC. This also will be explained later in detail.

[0008] In the above-described second prior art signal transmission circuit, however, the power consumption is still large. Also, since each signal transmission circuit requires two transmission lines, the signal transmission circuit is complex and large in scale.

[0009] A third prior art signal transmission circuit is constructed by precharging circuits for precharging the input and output, respectively, of a transmission line, in order to decrease the power consumption (see: JP-A-2001-156180). This also will be explained later in detail.

[0010] In the above-described third prior art signal transmission circuit, although the power consumption can be decreased, the precharging circuits are required, which would complicate and increase the circuit configuration in size.

SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide a simple signal transmission circuit capable of decreasing the power consumption even if the frequency of a transmitted signal is higher than 200 MHz, for example.

[0012] According to the present invention, a signal transmission circuit is formed by a transmitter, a receiver, a transmission line therebetween, and a bias circuit. The transmitter receives an input signal to transmit a signal corresponding to the input signal to the input of the transmission line. A voltage amplitude of the transmitted signal is smaller than a voltage amplitude defined by first and second power supply terminals. The receiver receives the transmitted signal, adjusts a voltage of the received signal in accordance with a bias voltage to generate a voltage adjusted signal, and wave-shapes the voltage adjusted signal to generate an output signal. The bias circuit differentially amplifies the output signal of the receiver and an inverted signal thereof to generate the bias voltage. The bias circuit includes a capacitor charged and discharged in accordance with the bias voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will be more clearly understood from the description set forth below, as compared with the prior art, with reference to the accompanying drawings, wherein:

[0014]FIG. 1 is a block circuit diagram illustrating a conventional LCD apparatus to which a signal transmission circuit is applied;

[0015]FIG. 2 is a circuit diagram illustrating a first prior art signal transmission circuit;

[0016]FIG. 3 is a circuit diagram illustrating a second prior art signal transmission circuit;

[0017]FIG. 4 is a timing diagram for explaining the operation of the circuit of FIG. 3;

[0018]FIG. 5 is a circuit diagram illustrating a third prior art signal transmission circuit;

[0019]FIG. 6 is a circuit diagram illustrating a first embodiment of the signal transmission circuit according to the present invention;

[0020]FIG. 7 is a timing diagram for explaining the operation of the circuit of FIG. 6;

[0021]FIG. 8 is a circuit diagram illustrating a second embodiment of the signal transmission circuit according to the present invention; and

[0022]FIG. 9 is a timing diagram for explaining the operation of the circuit of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Before the description of the preferred embodiments, prior art signal transmission circuits will be explained with reference to FIGS. 1, 2, 3, 4 and 5.

[0024] In FIG. 1, which illustrates a conventional LCD apparatus to which a signal transmission circuit is applied, reference numeral 101 designates an LCD panel having 1024×3×768 dots, for example. In this case, the LCD panel 101 includes 3072 (1024×3) data lines (or signal lines) DL and 768 gate lines (or scan lines) GL. One pixel, which is located at each intersection between the data lines DL and the gate lines GL, is constructed by one thin film transistor Q and one liquid crystal cell C.

[0025] In order to drive the 3072 data lines DL, eight data line driver circuits 102-1, 102-2, . . . , 102-8 formed by large scale integrated (LSI) circuits, each for driving the 384 data lines DL, are provided on a horizontal edge of the LCD panel 101. In this case, the data line driver circuits 102-1, 102-2, . . . , 102-8 are arranged by a cascade connection method to transmit a horizontal clock signal HCK, a horizontal start pulse signal HST, 8-bit digital data signals D1, D2, . . . , D8 and so on therethrough.

[0026] On the other hand, in order to drive the 768 gate lines GL, four gate line driver circuits 103-1, 103-2, 103-3 and 103-4 formed by LSIs are provided on a vertical edge of the LCD panel 101. In this case, the gate line driver circuits 103-1, 103-2, 103-3 and 103-4 are arranged by a cascade connection method to transmit a vertical clock signal VCK, a vertical start pulse signal VST and so on therethrough.

[0027] Also, a timing controller 4 formed by an LSI circuit is provided on the LCD panel 101 in proximity to the data line driver circuit 102-1 and the gate line driver circuit 103-1. In this case, the timing controller 104 generates the horizontal clock signal HCK, the horizontal start pulse signal HST, the data signals D1, D2, . . . , D8 and so on and transmits them to the data line driver circuit 102-1. Also, the timing controller 104 generates the vertical clock signal VCK, the vertical start pulse signal VST and so on and transmits them to the gate line driver circuit 103-1.

[0028] Recently, the data line driver circuits 102-1, 102-2,. . . , 102-8, the gate line driver circuits 103-1, 103-2, 103-3 and 103-4 and the timing controller 104 are mounted on the LCD panel 101 by a chips-on-glass (COG) process or a system-on-glass (SOG) process in order to decrease the manufacturing cost. In this case, transmission lines made of aluminum are formed on the LCD panel 101 between the data line driver circuits 102-1, 102-2, . . . , 102-8, the gate line driver circuits 103-1, 103-2, 103-3 and 103-4, and the timing controller 104.

[0029] Since the LCD apparatus of FIG. 1 is large in scale and high in precision, the above-mentioned transmission lines. particularly, the transmission lines between the data line driver circuits 102-1, 102-2, . . . , 102-8 need to be operated at high speed.

[0030] In FIG. 1, TX designates a transmitter circuit including a plurality of transmitters and RX designates a receiver circuit including a plurality of receivers. That is, one signal transmission circuit is constructed by one transmitter of the transmitter circuit TX, one receiver of the receiver circuit RX, and one transmission line therebetween.

[0031] In FIG. 2, which illustrates a first prior art signal transmission circuit, a transmitter TX₁ for receiving a horizontal clock signal HCK_(in) is constructed by a CMOS inverter formed by a P-channel MOS transistor Q_(p211) and an N-channel MOS transistor Q_(n211), and a receiver RX₁ for receiving the horizontal clock signal HCK_(in) to generate a horizontal clock signal HCK_(out) is constructed by a CMOS inverter formed by a P-channel MOS transistor Q_(P212) and an N-channel MOS transistor Q_(n212). The transmitter TX₁ and the receiver RX₁ are connected by a transmission line having a resistance of R₁. Also, a transmitter TX₂ for a horizontal start pulse signal HST_(in) is constructed by a CMOS inverter formed by a P-channel MOS transistor Q_(p221) and an N-channel MOS transistor Q_(n221), and a receiver RX₂ for receiving the horizontal start pulse signal HST_(in) to generate a horizontal start pulse signal HST_(out) is constructed by a CMOS inverter formed by a P-channel MOS transistor Q_(p221) and an N-channel MOS transistor Q_(n221). The transmitter TX₂ and the receiver RX₂ are connected by a transmission line having a resistance of R₂. Further, a transmitter TX₃ for receiving digital data D1 _(in) is constructed by a CMOS inverter formed by a P-channel MOS transistor Q_(n231) and an N-channel MOS transistor Q_(n231), and a receiver RX₃ for receiving the digital data D1 _(in) to generate digital data D1 _(out) is constructed by a CMOS inverter formed by a P-channel MOS transistor Q_(p232) and an N-channel MOS transistor Q_(n232). The transmitter TX₃ and the receiver RX₃ are connected by a transmission line having a resistance of R₃.

[0032] In FIG. 2, C_(p11), C_(p21), p₃₁, . . . are output parasitic capacitances of the transmitters TX₁, TX₂, TX₃, . . . , respectively, whose values are about 3 to 4 pF, and C_(p12), C_(p22), C_(p32), . . . are input parasitic capacitances of the receivers RX₁, RX₂, RX₃, . . . , respectively, whose values are about 3 to 4 pF.

[0033] Similar transmitters, receivers and transmission lines are provided for digital data D2, D3, . . . , D8 and so on.

[0034] For example, in the transmitter TX₁ when the horizontal clock signal HCK is low (=GND), the transistors Q_(p211) and Q_(n211) are turned ON and OFF, respectively, so that the output voltage is high (=V_(DD)). As a result, in the receiver RX₁, the input voltage is high (=V_(DD)) so that the transistors Q_(p221) and Q_(n221) are turned OFF and ON, respectively. Thus, the output voltage of the receiver RX₁ is high (=V_(DD)).

[0035] On the other hand, in the transmitter TX₁, when the horizontal clock signal HCK is high (=V_(DD)), the transistors Q_(p211) and Q_(n211) are turned OFF and ON, respectively, so that the output voltage is low (=GND). As a result, in the receiver RX₁, the input voltage is low (=GND) so that the transistors Q_(p221) and Q_(n221) are turned OFF and ON, respectively. Thus, the output voltage of the receiver RX₁ is low (=GND).

[0036] The horizontal clock signal HCK supplied to the input of the transmitter TX₁ is transmitted via the transmission line (R₁) to the output of the receiver RX₁.

[0037] Generally, the power consumption P(TX₁) of the transmitter TX₁ is represented by

P(TX ₁)∝f·C _(p11) ·V _(DD) ²

[0038] where f is the frequency of the horizontal clock signal HCK_(in).

[0039] Also the power consumption P(RX₁) of the receiver RX₁ is represented by

P(RX ₁)∝f·C _(P12) ·V _(DD) ²

[0040] Therefore, the higher the frequency f of the horizontal clock signal HCK, the larger the power consumption.

[0041] Thus, in FIG. 2, the higher the frequencies of the signals HCK, HST, D1, . . . , the higher the power consumption. Also, the transmitted signals are blunted by a time constant determined by the transmission line such as R₁ whose value is several hundreds of Ω as well as the output and input parasitic capacitances such as C_(p11) and C_(p12) whose values are about 3 to 4 pF.

[0042] In FIG. 3, which illustrates a second prior art signal transmission circuit, this signal transmission circuit uses a reduced swing differential signaling (RSDS) method in conformity with the interface standard of National Semiconductor Inc. A transmitter TX₁ for receiving a horizontal clock signal HCK_(in) and its inverted signal /HCK_(in) is constructedby a differential amplifier which generates two complemental output signals, and a receiver RX₁ for generating a horizontal clock signal HCK_(out) is constructed by a voltage comparator which compares the voltage of one of the complemental output signals of the transmitter TX₁ with that of the other. The transmitter TX₁ and the receiver RX₁ are connected by two transmission lines having resistances R₁ and /R₁, respectively, with a terminal resistor R_(t1). Also, a transmitter TX₂ for receiving a horizontal start pulse signal HST_(in) and its inverted signal /HST_(in) is constructed by a differential amplifier which generates two complementary output signals, and a receiver RX₂ for generating a horizontal start pulse signal HST_(out) is constructed by a voltage comparator which compares the voltage of one of the complementary output signals of the transmitter TX₂ with that of the other. The transmitter TX₂ and the receiver RX₂ are connected by two transmission lines having resistances R₂ and /R₂, respectively, with a terminal resistor R_(t2). Further, a transmitter TX₃ for receiving digital data D1 _(in) and its inverted signal /D1 _(in) is constructed by a differential amplifier which generates two complementary output signals, and a receiver RX₃ for generating digital data D1 _(out) is constructed by a voltage comparator which compares the voltage of one of the complementary output signals of the transmitter TX₃ with that of the other. The transmitter TX₃ and the receiver RX₃ are connected by two transmission lines having resistances R₃ and /R₃, respectively, with a terminal resistor R_(t3).

[0043] Similar transmitters, receivers and transmission lines with terminal resistors are provided for digital data D2, D3, . . . , D8 and so on.

[0044] For example, as shown in FIG. 4, when one output signal S₁ of the transmitter TX₁ is changed, one input signal S₁′ of the receiver RX₁ is blunted by a time constant determined by the transmission line (R₁) and the terminal resistor R_(t1) as well as output and input parasitic capacitances (not shown). Therefore, when the frequency of the clock signal HCK_(in) is very high, the input signal S₁′ cannot reach a high level.

[0045] Also, in FIG. 3, since each of the transmitters TX₁, TX₂, TX₃, . . . requires a current of 2.0 mA and each of the receivers RX₁, RX₂, RX₃, . . . requires a current of several hundreds of μA, the power consumption is still large.

[0046] Further, since each signal transmission circuit requires two transmission lines, the signal transmission circuit is complex and large in scale.

[0047] In FIG. 5, which illustrates a third prior art signal transmission circuit (see: JP-A-2001-156180), a transmitter TX₁ for receiving a horizontal clock signal HCK_(in) is constructed by a transfer gate TG₁ clocked by clock signals φ_(p) and / φ_(p), a precharging N-channel MOS transistor Q_(n511) powered by a voltage V_(p) and clocked by the clock signal φ_(p), and N-channel MOS transistors Q_(n512) and Q_(n513), and a receiver RX₁ for receiving the horizontal clock signal HCK₁ to generate a horizontal clock signal HCK_(out) is constructed by a precharging P-channel MOS transistor Q_(n511) powered by a power supply voltage V_(DD) and clocked by the clock signal / φ_(p), an N-channel MOS transistor Q_(n514), a bias circuit formed by a P-channel MOS transistor Q_(n514) and an N-channel MOS transistor Q_(n515) powered by a bias voltage VB and the ground voltage GND clocked by the clock signal φ_(p), and an inverter I₁. The transmitter TX₁ and the receiver RX₁ are connected by a transmission line having a resistance of R₁. Also, a transmitter TX₂ for receiving a horizontal start pulse signal HST is constructed by a transfer gate TG₂ clocked by clock signals φ_(p) and / φ_(p), a precharging N-channel MOS transistor Q_(n521) powered by the voltage V_(p) and clocked by the clock signal φ_(p), and N-channel MOS transistors Q_(n522) and Q_(n523), and a receiver RX₂ for receiving the horizontal start pulse signal HST_(in) to generate a horizontal start pulse signal HST_(out) is constructed by a precharging P-channel MOS transistor Q_(p521) powered by the power supply voltage V_(DD) and clocked by the clock signal / φ_(p), an N-channel MOS transistor Q_(n524), a bias circuit formed by a P-channel MOS transistor Q_(p522) and an N-channel MOS transistor Q_(n525) powered by the bias voltage VB and the ground voltage GND clocked by the clock signal φ_(p), and an inverter I₂. The transmitter TX₂ and the receiver RX₂ are connected by a transmission line having a resistance of R₂. Further, a transmitter TX₃ for receiving digital data D1 _(in) is constructed by a transfer gate TG₃ clocked by clock signals φ_(p) and / φ_(p), a precharging N-channel MOS transistor Q_(n531) powered by the voltage V_(p) and clocked by the clock signal φ_(p), and N-channel MOS transistors Q_(n532) and Q_(n533), and a receiver RX₃ for receiving the digital data D1 _(in) to generate digital data D1 _(out) is constructed by a precharging P-channel MOS transistor Q_(n531) powered by the power supply voltage V_(DD) and clocked by the clock signal / φ_(p), an N-channel MOS transistor Q_(n534), a bias circuit formed by a P-channel MOS transistor Q_(p532) and an N-channel MOS transistor Q_(n535) powered by the bias voltage VB and the ground voltage GND clocked by the clock signal φ_(p), and an inverter I₃. The transmitter TX₃ and the receiver RX₃ are connected by a transmission line having a resistance of R₃.

[0048] Similar transmitters, receivers and transmission lines are provided for digital data D2, D3, . . . , D8 and so on.

[0049] The operation of the transmitter TX₁ and the receiver RX₁ is explained next.

[0050] During a precharging period, the clock signals φ_(p) and / φ_(p) are high and low, respectively. Therefore, in the transmitter TX₁, the transfer gate TG₁ is closed and the transistor Q_(n513) is turned ON, so that the transistor Q_(n512) is turned OFF. Also, the precharging transistor Q_(n511) is turned ON. As a result, the input of the transmission line (R₁) is charged to V_(p). On the other hand, in the receiver RX₁, the transistors Q_(p512) and Q_(n515) are turned ON and OFF, respectively, to turn OFF the transistor Q₅₁₄. Also, the precharging transistor Q_(p511) is turned ON. As a result, the input of the inverter I₁ is charged to V_(DD), so that the output signal HCK_(out) of the inverter I₁ is low.

[0051] When the control enters a transmission period where the horizontal clock signal HCK_(in) is high, the clock signals φ_(p) and / φ_(p) are low and high, respectively. Therefore, in the transmitter TX₁, the transfer gate TG₁ is opened and the transistor Q_(n513) is turned OFF, so that the transistor Q_(n512) is turned ON by the horizontal clock signal HCK_(in) passed through the transfer gate TG₁. Also, the precharging transistor Q_(n511) is turned OFF. As a result, the voltage at the input of the transmission line (R₁) is decreased, so that the voltage at the output of the transmission line (R₁) is decreased. On the other hand, in the receiver RX₁, the transistors Q_(p512) and Q_(p515) are turned OFF and ON, respectively, so that the gate voltage of the transistor Q_(n514) is biased at VB. Also, the precharging transistor Q_(p311) is turned OFF. As a result, the input of the inverter I₁ is discharged through the biased transistor Qn_(n514) to invert the output signal HCK_(out) of the inverter I₁ from low to high. Contrary to the above, when the control enters a transmission period where the horizontal clock signal HCK is low, the clock signals φ_(p) and / φ_(p) are low and high, respectively. Therefore, in the transmitter TX₁, the transfer gate TG₁ is opened and the transistor Q_(n513) is turned OFF, so that the transistor Q_(n512) remains in an OFF state by the horizontal clock signal HCK_(in) passed through the transfer gate TG₁. Also, the precharging transistor Q_(n511) is turned OFF. As a result, the voltage at the input of the transmission line (R₁) is not decreased, so that the voltage at the output of the transmission line (R₁) is not decreased. On the other hand, in the receiver RX₁, the transistors Q _(p512) and Q_(n515) are turned ON and OFF, respectively, so that the gate voltage of the transistor Q_(n514) is biased at GND. Also, the precharging transistor Q_(p511) is turned OFF. As a result, the input of the inverter I₁ is not discharged through the biased transistor Q_(n314) so that the output signal HCK_(out) of the inverter I₁ remains low.

[0052] Thus, in the signal transmission circuit of FIG. 5, since currents flow when transmitting a high level signal but currents hardly flow when transmitting a low level signal, the power consumption can be decreased.

[0053] In the signal transmission circuit of FIG. 5, however, since the precharging circuits formed by the transistors Q_(n511) and Q_(n511), and the bias circuit (Q_(p512), Q_(n515)) are required, the control circuit (not shown) therefor is complex. Also, when the output signal of the transmitter such as TX₁ is low, the input signal of the receiver such as RX₁ is blunted by a time constant determined by the transmission line (R₁) as well as output and input parasitic capacitances (not shown).

[0054] In FIG. 6, which illustrates a first embodiment of the signal transmission circuit according to the present invention, a transmitter TX₁ for receiving a horizontal clock signal HCK_(in) is constructed by a CMOS inverter formed by a P-channel MOS transistor Q_(p11) and an N-channel MOS transistor Q_(n11) and a voltage amplitude limiting N-channel MOS transistor Q_(n12) connected between the transistors Q_(p11) and Q_(n11). In this case, a definite bias voltage VB₁ is applied to the gate of the transistor Q_(n12) to limit a high level of an output signal. For example, the high level of the output signal is limited by about 1V lower than a power. supply voltage VDD such as 2.5V. Also, a receiver RX₁ for receiving the horizontal clock signal HCK_(in) to generate a horizontal clock signal HCK_(out) is constructed by a load drain-gate connected P-channel MOS transistor Q_(p12), a constant current source formed by an N-channel MOS transistor Q_(n13) whose gate receives a definite bias voltage VB₂, and a voltage adjusting N-channel MOS transistor Q_(n14) whose gate receives a variable bias voltage VB₃. The voltage adjusting N-channel MOS transistor Q_(n14) adjusts the voltage at node N₁₁ to generate an adjusted voltage at node N_(n12). In this case, the higher the bias voltage VB₃, the higher the voltage at node N₁₂. Also, the transistors Q_(p12), Q_(n14) and Q_(n13) entirely serve as a current limiting means. The voltage at node N₁₂ is supplied to an inverter INV₁₁ for wave-shaping the voltage at node N₁₂, and is inverted by an inverter INV₁₂. In this case, since the inverter INV₁₁ has a threshold voltage such as 0.2V, the voltage at node N₁₂ is changed to a high level signal (=V_(DD)) or a low level signal (=GND) in accordance with whether or not the voltage at node N₁₂ is higher than the threshold voltage. The transmitter TX₁ and the receiver RX₁ are connected by a transmission line having a resistance of R₁ whose value is hundreds of Ω.

[0055] Also, a transmitter TX₂ for receiving a horizontal start pulse signal HST_(in) is constructed by a CMOS inverter formed by a P-channel MOS transistor Q_(p21) and an N-channel MOS transistor Q_(n21) and a voltage amplitude limiting N-channel MOS transistor Q_(n22) connected between the transistors Q_(p21) and Q_(n21). In this case, the definite bias voltage VB₁ is applied to the gate of the transistor Q_(n22) to limit a high level of an output signal. For example, the high level of the output signal is limited by about 1V lower than a power supply voltage V_(DD) such as 2.5V. Also, a receiver RX₂ for receiving the horizontal start pulse signal HST_(in) to generate a horizontal clock signal HST_(out) is constructed by a load drain-gate connected P-channel MOS transistor Q_(p22), a constant current source formed by an N-channel MOS transistor Q_(n23) whose gate receives the definite bias voltage VB₂, and a voltage adjusting N-channel MOS transistor Q_(n24) whose gate receives the variable bias voltage VB₃. The voltage adjusting N-channel MOS transistor Q_(n24) adjusts the voltage at node N₂₁ to generate an adjusted voltage at node N₂₂. In this case, the higher the bias voltage VB₃, the higher the voltage at node N₂₂. Also, the transistors Q_(p22), Q_(n24) and Q_(n23) entirely serve as a current limiting means. The voltage at node N₂₂ is supplied to an inverter INV₂₁ for wave-shaping the voltage at node N₂₂, and is inverted by an inverter INV₂₂. In this case, since the inverter INV₂₁ has a threshold voltage such as 0.2V, the voltage at node N₂₂ is changed to a high level signal (=V_(DD)) or a low level signal (=GND) in accordance with whether or not the voltage at node N₂₂ is higher than the threshold voltage. The transmitter TX₂ and the receiver RX₂ are connected by a transmission line having a resistance of R₂ whose value is hundreds of Ω.

[0056] Further, a transmitter TX₃ for receiving digital data D1 _(in) is constructed by a CMOS inverter formed by a P-channel MOS transistor Q_(p31) and an N-channel MOS transistor Q_(n31) and a voltage amplitude limiting N-channel MOS transistor Q_(n32) connected between the transistors Q_(p31), and Q_(n31). In this case, the definite bias voltage VB₁ is applied to the gate of the transistor Q_(n32) to limit a high level of an output signal. For example, the high level of the output signal is limited by about 1V lower than a power supply voltage V_(DD) such as 2.5V. Also, a receiver RX₃ for receiving the digital data D1 _(in) to generate digital data D1 _(out) is constructed by a load drain-gate connected P-channel MOS transistor Q_(p32), a constant current source formed by a N-channel MOS transistor Q_(n33) whose gate receives the definite bias voltage VB₂, and a voltage adjusting N-channel MOS transistor Q_(n34) whose gate receives the variable bias voltage VB₃. The voltage adjusting N-channel MOS transistor Q_(n34) adjusts the voltage at node N₃₁ to generate an adjusted voltage at node N₃₂. In this case, the higher the bias voltage VB₃, the higher the voltage at node N₃₂. Also, the transistors Q_(p32), Q_(n34) and Q_(n33) entirely serve as a current limiting means. The voltage at node N₃₂ is supplied to an inverter INV₃₁ for wave-shaping the voltage at node N₃₂, and is inverted by an inverter INV₃₂. In this case, since the inverter INV₃₁ has a threshold voltage such as 0.2V, the voltage at node N₁₂ is changed to a high level signal (=V_(DD)) or a low level signal (=GND) in accordance with whether or not the voltage at node N₃₂ is higher than the threshold voltage. The transmitter TX₃ and the receiver RX₃ are connected by a transmission line having a resistance of R₃ whose value is hundreds of Ω.

[0057] Similar transmitters, receivers and transmission lines are provided for digital data D2, D3, . . . , D8 and so on.

[0058] A bias circuit BC receives the horizontal clock signal HCK_(out) from the receiver RX₁ and transmits the bias voltage VB₃ to the gates of the voltage adjusting transistors Q_(n14), Q_(n24), Q_(n34), . . . , of the receivers RX₁, RX₂, RX₃, . . . .

[0059] The bias circuit BC is constructedby a differential amplifier DA for differentially amplifying the horizontal clock signal HCK_(out) and its inverted signal, and a capacitor C_(o) charged and discharged by the differential amplifier DA. The differential amplifier DA is formed by a differential pair including P-channel MOS transistors Q_(p01) and Q_(p02) controlled by the horizontal clock signal HCK_(out) and its inverted signal, respectively, a current mirror circuit formed by N-channel MOS transistors Q_(n01) and Q_(n02), and a switch formed by an N-channel MOS transistor Q_(n03). Note that the transistors Q_(p01) and Q_(p02) have the same dimension, and the transistors Q_(n0) and Q_(n1) have the same dimension, in order to respond to the horizontal clock signal HCK_(out) which has a 50% duty ratio. Also, the transistor Q_(n03) is controlled by the bias voltage VB₃, in order to prevent the receiver RX₁ from self-oscillating.

[0060] The operation of the signal transmission circuit of FIG. 6 is explained next with reference to FIG. 7, where V_(DD) is 2.5V, the frequency of the horizontal clock signal HCK is 250 MH_(z), and the resistances R₁, R₂, R₃, . . . are 100 Ω.

[0061] First, at time t0, in the transmitter TX₁, when the horizontal clock signal HCK_(in) is low (=GND), the transistors Q_(p11) and Q_(n11) are turned ON and OFF, respectively, so that the output voltage is high (=VB₁−V_(GS), where V_(GS) is a gate-to-source voltage of the transistor Q_(n12)). For example, if VB₁ is 2.0V and V_(GS) is 0.8V, VB₁−V_(GS)=1.2V. As a result, in the receiver RX₁, the voltage at node N₁₁ is high (=1.2V). In this case, since the voltage at node N₁₂ is sufficiently higher than the threshold voltage (=0.2V) of the inverter INV₁₁, the horizontal clock signal HCK_(out) is high (=V_(DD)) Therefore, in the bias circuit BC, the transistors Q_(p01) and Q_(p02) are turned OFF and ON, respectively, the capacitor C₀ is charged to V_(DD), so that the bias voltage VB₃ is high (=V_(DD)).

[0062] Next, at time t1, the horizontal clock signal HCK_(in) is supplied to the transmitter TX₁. As a result, in the receiver RX₁, the voltage at node N₁₁ is rapidly decreased, so that the voltage at node N₁₂ may become lower than the threshold voltage (=0.2V) of the inverter INV₁₁. Thus, the horizontal clock signal HCK_(out) is low (=0V). Therefore, in the bias circuit BC, the transistors Q_(p01) and Q_(p02) are turned ON and OFF, respectively, the capacitor C₀ is gradually discharged, so that the bias voltage VB₃ is gradually decreased.

[0063] When the bias voltage VB₃ is gradually decreased, the voltage at node N₁₁ is adjusted by the transistor Q_(n14) to increase the voltage at node N₁₂ Finally, at time t2, the voltage at node N₁₂ reaches the threshold voltage (=0.2V) of the inverter INV₁₁, so that the bias voltage VB₃ is converged to a definite value such as 1.6V.

[0064] Next, at time t3 when a period of time has sufficiently lapsed after time t2, a horizontal start pulse signal HST_(in), digital data D1 _(in) and so on are supplied to the transmitters TX₂, TX₃, . . . . As a result, since the bias voltage VB₃ is supplied commonly to the receivers RX₂, RX₃, . . . , the voltages at nodes N₂₁, N₃₁, . . . are immediately changed, so that a horizontal clock signal HST_(out), digital data D1 _(out) and so on can be optimally regenerated or received.

[0065] In FIG. 6, since the bias voltage VB₃ is optimally supplied to the receivers RX₁, RX₂, RX₃, . . . , the transmission of signals can be at a higher frequency than 200 MHz. Also, since each of the transmitters TX₁, TX₂, TX₃, . . . has a voltage amplitude limiting function, the power consumption therein can be decreased. Note that this power consumption is in proportion to the squared voltage amplitude. Further, since each of the receivers RX₁, RX₂, RX₃, . . . has a current limiting function and a voltage adjusting function, the power consumption therein can be decreased. Note that this power consumption is in proportion to the current and the squared voltage amplitude. Additionally, since the transistors Q_(p112) and Q_(n14) of the receiver such as RX₁ serve as a current limiting means (several k Ω), when the transistor Q_(n11) is turned ON, a current flowing through the transmission line (R₁) is very small (about 1 mA), which also would decrease the power consumption.

[0066] Additionally, since the bias voltage VB₃ derived from a steady signal, i.e., the horizontal clock signal HCK_(out) is supplied to all the receivers RX₁, RX₂, RX₃, . . . , a non-steady signal such as a horizontal start pulse signal HST can be optimally received at a high frequency. Also, if the relative errors of the transmission lines (R₁, R₂, R₃, . . . ) are small, a wide operation range can be obtained even when the absolute errors of the transmission lines (R₁, R₂, R₃, . . . ) are large.

[0067] In FIG. 8, which illustrates a second embodiment of the signal transmission circuit according to the present invention, a transmitter TX₁′ for receiving a horizontal clock signal HCK_(in) is constructed by a CMOS inverter formed by a P-channel MOS transistor Q_(p11)′ and an N-channel MOS transistor Q_(n11)′ and a voltage amplitude limiting P-channel MOS transistor Q_(p12)′ connected between the transistors Q_(p11)′ and Q_(n11)′ . In this case, a definite bias voltage VB₁′ is applied to the gate of the transistor Q_(p12)′ to limit a low level of an output signal. For example, the low level of the output signal is limited by about 1.5V higher than a ground voltage GND such as 0V. Also, a receiver RX₁′ for receiving the horizontal clock signal HCK_(in) to generate a horizontal clock signal HCK_(out) is constructed by a load drain-gate connected N-channel MOS transistor Q_(n12)′, a constant current source formed by a P-channel MOS transistor Q₁₃′ whose gate receives a definite bias voltage VB₂′, and a voltage adjusting P-channel MOS transistor Q_(p14)′ whose gate receives a variable bias voltage VB₃′. The voltage adjusting P-channel MOS transistor Q_(p14)′ adjusts the voltage at node N₁₁′ to generate an adjusted voltage at node N₁₂′. In this case, the lower the bias voltage VB₃′, the higher the voltage at node N₁₂′. Also, the transistors Q_(n12)′, Q_(p14)′ and Q_(p13)′ entirely serve as a current limiting means. The voltage at node N₁₂′ is supplied to an inverter INV₁₁′ for wave-shaping the voltage at node N₁₂′ and is inverted by an inverter INV₁₂′. In this case, since the inverter INV₁₁′ has a threshold voltage such as 2.3V, the voltage at node N₁₂′ is changed to a low level signal (=GND) or a low level signal (=V_(DD)) in accordance with whether or not the voltage at node N₁₂′ is lower than the threshold voltage. The transmitter TX₁′ and the receiver RX₁′ are connected by a transmission line having a resistance of R₁ whose value is hundreds of Ω.

[0068] Also, a transmitter TX₂′ for receiving a horizontal start pulse HST_(in) is constructed by a CMOS inverter formed by a P-channel MOS transistor Q₂₁′ and an N-channel MOS transistor Q_(n21)′ and a voltage amplitude limiting P-channel MOS transistor Q_(p22)′ connected between the transistors Q_(p21)′ and Q_(n21)′. In this case, the definite bias voltage VB₁′ is applied to the gate of the transistor Q_(p22)′ to limit a low level of an output signal. For example, the low level of the output signal is limited by about 1.5V higher than the ground voltage GND such as 0V. Also, a receiver RX₂′ for receiving the horizontal start pulse signal HST_(in) to generate a horizontal clock signal HST_(out) is constructed by a load drain-gate connected N-channel MOS transistor Q_(n22)′, a constant current source formed by a P-channel MOS transistor Q_(p23)′ whose gate receives the definite bias voltage VB₂′, and a voltage adjusting P-channel MOS transistor Q_(p24)′ whose gate receives the variable bias voltage VB₃′. The voltage adjusting P-channel MOS transistor Q_(p24)′ adjusts the voltage at node N₂′ to generate an adjusted voltage at node N₂₂′. In this case, the lower the bias voltage VB₃′, the higher the voltage at node N₂₂′. Also, the transistors Q,_(n22)′, Q_(p24)′ and Q_(p23)′ entirely serve as a current limiting means. The voltage at node N₂₂′ is supplied to an inverter INV₂₁′ for wave-shaping the voltage at node N₂₂′, and is inverted by an inverter INV₂₂′. In this case, since the inverter INV₂₁′ has a threshold voltage such as 2.3V, the voltage at node N₂₂′ is changed to a low level signal (=GND) or a high level signal (=V_(DD)) in accordance with whether or not the voltage at node N₂₂′ is lower than the threshold voltage. The transmitter TX₂′ and the receiver RX₂′ are connected by a transmission line having a resistance of R₂′ whose value is hundreds of Ω.

[0069] Further, a transmitter TX₃′ for receiving digital data D1 _(in) is constructed by a CMOS inverter formed by a P-channel MOS transistor Q_(p31)′ and an N-channel MOS transistor Q_(n31)′ and a voltage amplitude limiting P-channel MOS transistor Q_(p32)′ connected between the transistors Q_(p31)′ and Q_(n31)′. In this case, the definite bias voltage VB₁′ is applied to the gate of the transistor Q_(p32)′ to limit a low level of an output signal. For example, the low level of the output signal is limited by about 1.5V lower than a ground voltage GND such as 0V. Also, a receiver RX₃′ for receiving the digital data D1 _(in) to generate digital data D1 _(out) is constructed by a load drain-gate connected N-channel MOS transistor Q_(n32)′, a constant current source formed by a P-channel MOS transistor Q_(p33)′ whose gate receives the definite bias voltage VB₂′, and a voltage adjusting P-channel MOS transistor Q_(p34)′ whose gate receives the variable bias voltage VB₃′. The voltage adjusting P-channel MOS transistor Q_(p34)′ adjusts the voltage at node N₃₁′ to generate an adjusted voltage at node N₃₂′. In this case, the lower the bias voltage VB₃′, the higher the voltage at node N₃₂′. Also, the transistors Q_(n32)′, Q_(p34)′ and Q_(p33)′ entirely serve as a current limiting means. The voltage at node N₃₂′ is supplied to an inverter INV₃₁′ for wave-shaping the voltage at node N₃₂′, and is inverted by an inverter INV₃₂′. In this case, since the inverter INV₃₁′ has a threshold voltage such as 2.3V, the voltage at node N₃₂′ is changed to a low level signal (=GND) or a high level signal (=VDD) in accordance with whether or not the voltage at node N₃₂′ is lower than the threshold voltage. The transmitter TX₃′ and the receiver RX₃′ are connected by a transmission line having a resistance of R₃ whose value is hundreds of Ω.

[0070] Similar transmitters, receivers and transmission lines are provided for digital data D2, D3, . . . , D8 and so on.

[0071] A bias circuit BC′ receives the horizontal clock signal HCK_(out) from the receiver RX₁′ and transmits the bias voltage VB₃′ to the gates of the voltage adjusting transistors Q_(p14)′, Q_(p24)′, Q_(p34), . . . , of the receivers RX₁′, RX₂′, RX₃′, . . . .

[0072] The bias circuit BC′ is constructed by a differential amplifier DA′ for differentially amplifying the horizontal clock signal HCK_(out) and its inverted signal, and a capacitor C_(o)′ charged and discharged by the differential amplifier DA′. The differential amplifier DA′ is formed by a differential pair including N-channel MOS transistors Q_(n01)′ and Q_(n02)′ controlled by the horizontal clock signal HCK_(out) and its inverted signal, respectively, a current mirror circuit formed by P-channel MOS transistors Q_(p01)′ and Q_(p02)′, and a switch formed by a P-channel MOS transistor Q_(p03)′. Note that the transistors Q_(n01′ and Q) _(n02)′ have the same dimension, and the transistors Q_(p01)′ and Q_(p02)′ have the same dimension, in order to respond to the horizontal clock signal HCK_(out) which has a 50% duty ratio. Also, the transistor Q_(p03)′ is controlled by the bias voltage VB₃′, in order to prevent the receiver RX₁′ from self-oscillating.

[0073] The operation of the signal transmission circuit of FIG. 8 is explained next with reference to FIG. 9, where V_(DD) is 2.5V, the frequency of the horizontal clock signal HCK is 250 MH_(z), and the resistances R₁, R₂, R₃, . . . are 100 Ω.

[0074] First, at time t0, in the transmitter TX₁′, when the horizontal clock signal HCKin is high (=V_(DD)), the transistors Q_(p11)′ and Q_(n11)′ are turned OFF and ON, respectively, so that the output voltage is low (=VB₁′+V_(GS), where V_(GS) is a gate-to-source voltage of the transistor Q_(p12)′). For example, if VB₁′ is 0.5V and V_(GS) is 0.8V, VB₁′+V_(GS)=1.3V. As a result, in the receiver RX₁′, the voltage at node N₁₁′ is low (=1.3V). In this case, since the voltage at node N₁₂′ is sufficiently lower than the threshold voltage (=2.3V) of the inverter INV₁₁′, the horizontal clock signal HCK_(out) is low (=GND). Therefore, in the bias circuit BC′, the transistors Q_(n01)′ and Q_(n02)′ are turned OFF and ON, respectively the capacitor C₀′ is discharged to GND, so that the bias voltage VB₃′ is low (=GND).

[0075] Next, at time t1, the horizontal clock signal HCK_(in) is supplied to the transmitter TX₁′. As a result, in the receiver RX₁′, the voltage at node N₁₂′ is rapidly increased, so that the voltage at node N₁₂′ may become higher than the threshold voltage (=2.3V) of the inverter INV₁₁′. Thus, the horizontal clock signal HCK_(out) is high (=V_(DD)). Therefore, in the bias circuit BC′, the transistors Q_(n01)′ and Q_(n02)′ are turned ON and OFF, respectively, the capacitor C₀′ is gradually charged, so that the bias voltage VB₃′ is gradually increased.

[0076] When the bias voltage VB₃′ is gradually decreased, the voltage at node N₁₁′ is adjusted by the transistor Q_(p14)′ to increase the voltage at node N₁₂′. Finally, at time t2, the voltage at node N₁₂′ reaches the threshold voltage (=2.3V) of the inverter INV₁₁′, so that the bias voltage VB₃′ is converged to a definite value such as 0.9V.

[0077] Next, at time t3 when a period of time has sufficiently lapsed after time t2, a horizontal start pulse signal HST_(in), digital data D1 _(in) and so on are supplied to the transmitters TX₂′, TX₃′, . . . . As a result, since the bias voltage VB₃′ is supplied commonly to the receivers RX₂′, RX₃′, . . . , the voltages at nodes N₂₁′, N₃₁′, . . . are immediately changed, so that a horizontal clock signal HST_(out), digital data D1 _(out) and so on can be optimally regenerated or received.

[0078] In FIG. 8, since the bias voltage VB₃′ is optimally supplied to the receivers RX₁′, RX₂′, RX₃′, . . . , the transmission of signals can be at a higher frequency than 200 MHz. Also, since each of the transmitters TX₁′, TX₂′, TX₃′, . . . has a voltage amplitude limiting function, the power consumption therein can be decreased. Note that this power consumption is in proportion to the squared voltage amplitude. Further, since each of the receivers RX₁′, RX₂′, RX₃′, . . . has a current limiting function and a voltage adjusting function, the power consumption therein can be decreased. Note that this power consumption is in proportion to the current and the squared voltage amplitude. Additionally, since the transistors Q_(n12)′ and Q_(p14)′ of the receiver such as RX₁′ serve as a current limiting means (several k Ω), when the transistor Q_(p11)′ is turned ON, a current flowing through the transmission line (R₁) is very small (about 1 mA), which also would decrease the power consumption.

[0079] Additionally, since the bias voltage VB₃′ derived from a steady signal, i.e., the horizontal clock signal HCK_(out) is supplied to all the receivers RX₁′, RX₂′, RX₃′, . . . , a non-steady signal such as a horizontal start pulse signal HST can be optimally received at a high frequency. Also, if the relative errors of the transmission lines R₁, R₂, R₃, . . . are small, a wide operation range can be obtained even when the absolute errors of the transmission lines R₁, R₂, R₃, . . . are large.

[0080] In FIGS. 6 and 8, although the bias circuit BC or BC′ is provided to complicate the signal transmission circuit, only one bias circuit BC or BC′ is provided commonly for all the receivers RX₁, RX₂, RX₃, . . . or RX₁′, RX₂′, RX₃′, . . . , so that the signal transmission circuit is hardly complicated.

[0081] As explained hereinabove, according to the present invention, a simple signal transmission circuit capable of decreasing the power consumption can be obtained. 

1. A signal transmission circuit comprising: first and second power supply lines; a first transmission line; a first transmitter, connected to an input of said first transmission line and powered by said first and second power supply terminals, for receiving a first input signal to transmit a signal corresponding to said first input signal to the input of said first transmission line, a voltage amplitude of said transmitted signal being smaller than a voltage amplitude defined by said first and second power supply terminals; a first receiver, connected to an output of said first transmission line and powered by said first and second power supply terminals, for receiving said transmitted signal, adjusting a voltage of said received signal in accordance with a bias voltage to generate a voltage adjusted signal, and wave-shaping said voltage adjusted signal to generate a first output signal; and a bias circuit, connected to said first receiver and powered by said first and second power supply terminals, for differentially amplifying said first output signal and an inverted signal thereof to generate said bias voltage, said bias circuit including a capacitor charged and discharged in accordance with said bias voltage.
 2. The signal transmission circuit as set forth in claim 1, wherein said first receiver increases or decreases a difference between the voltage of said received signal and the voltage of said voltage adjusted signal in accordance with a change of said bias voltage.
 3. The signal transmission circuit as set forth in claim 1, wherein said first transmitter comprises: a first P-channel MOS transistor having a source connected to said first power supply terminal, a gate for receiving said first input signal, and a drain; a first N-channel MOS transistor having a source connected to said second power supply terminal, a gate for receiving said first input signal, and a drain connected to the input of said first transmission line; a second N-channel MOS transistor connected between the drain of said first P-channel MOS transistor and the drain of said first N-channel MOS transistor, a definite voltage being applied to a gate of said second N-channel MOS transistor.
 4. The signal transmission circuit as set forth in claim 3, wherein said first receiver comprises: a load connected to said first power supply terminal; a current source connected to said second power supply terminal; a third N-channel MOS transistor, connected between said load and said current source, said third N-channel MOS transistor having a gate for receiving said bias voltage; and a wave-shaper, connected to a node between said load and said third N-channel MOS transistor and powered by said first and second power supply terminals, for comparing a voltage at said node with a threshold voltage.
 5. The signal transmission circuit as set forth in claim 4, wherein said first receiver further comprises an inverter connected to said wave-shaper.
 6. The signal transmission circuit as set forth in claim 5, wherein said bias circuit further includes: second and third P-channel MOS transistor, connected to said first power supply terminal and controlled by said first output signal and its inverted signal, respectively; a current mirror circuit formed by fourth and fifth N-channel MOS transistors having an input connected to said second P-channel MOS transistor and output connected to said third P-channel MOS transistor and said capacitor; and a sixth N-channel MOS transistor connected between said current mirror circuit and said second power supply terminal, said capacitor being connected to said second power supply terminal.
 7. The signal transmission circuit as set forth in claim 1, wherein said first transmitter comprises: a first P-channel MOS transistor having a source connected to said first power supply terminal, a gate for receiving said first input signal, and a drain connected to the input of said first transmission line; a first N-channel MOS transistor having a source connected to said second power supply terminal, a gate for receiving said first input signal, and a drain; a second P-channel MOS transistor connected between the drain of said first P-channel MOS transistor and the drain of said first N-channel MOS transistor, a definite voltage being applied to a gate of said second P-channel MOS transistor.
 8. The signal transmission circuit as set forth in claim 7, wherein said first receiver comprises: a load connected to said second power supply terminal; a current source connected to said first power supply terminal; a third P-channel MOS transistor, connected between said load and said current source, said third P-channel MOS transistor having a gate for receiving said bias voltage; and a wave-shaper, connected to a node between said load and said third P-channel MOS transistor and powered by said first and second power supply terminals, for comparing a voltage at said node with a threshold voltage.
 9. The signal transmission circuit as set forth in claim 8, wherein said first receiver further comprises an inverter connected to said wave-shaper.
 10. The signal transmission circuit as set forth in claim 9, wherein said bias circuit further includes: second and third N-channel MOS transistor, connected to said second power supply terminal and controlled by said first output signal and its inverted signal, respectively; a current mirror circuit formed by fourth and fifth P-channel MOS transistors having an input connected to said second N-channel MOS transistor and output connected to said third N-channel MOS transistor and said capacitor; and a sixth P-channel MOS transistor connected between said current mirror circuit and said first power supply terminal, said capacitor being connected to said first power supply terminal.
 11. The signal transmission circuit as set forth in claim 1, further comprising: at least one second transmission line; at least one second transmitter, connected to an input of said second transmission line and powered by said first and second power supply terminals, for receiving a second input signal to transmit a signal corresponding to said second input signal to the input of said second transmission line, a voltage amplitude of said transmitted signal being smaller than a voltage amplitude defined by said first and second power supply terminals; at least one second receiver, connected to an output of said second transmission line and powered by said first and second power supply terminals, for receiving said transmitted signal, adjusting a voltage of said received signal in accordance with said bias voltage to generate a voltage adjusted signal, and wave-shaping said voltage adjusted signal to generate a second output signal.
 12. The signal transmission circuit as set forth in claim 11, wherein said second transmitter has the same configuration as said first transmitter, and said second receiver has the same configuration as said first receiver. 